Recently, the solid connection at is coming up as an alternative for the hanging connection at a. The idea is, that after White's attachment at b, Black's defense at c is impossible. Thus, White is more or less guaranteed the option of playing either at b or d.
Because the corner is quite large, is a common move. White concludes a simple joseki with
, but she can also play tenuki. As of Jan 2003, up to
is very fashionable in pro games.
Black could also play the hane at . This diagram shows one possible continuation. Instead of
, White a-
-White tenuki is also possible.
As stated, the advantage for White over the hanging connection is that after White a, Black will have no choice but to answer at b.
-- AndreEngels